Speed control mechanism for grinding machines



Oct. 6, 1936. H. A. SILVEN 2,056,871

SPEED CONTROL MECHANISM FOR GRINDING MACHINES Filed NOV. 29, 1932 7o mun 1 72 V 6'8 5 ,r

' HERBERT/4. S/LVEN 77 V 73 w v l n .35 6 3s Patented Oct. 6, 1936 UNITED STATES PATENT OFFICE SPEED CONTROL MECHANISM FOR GRINDING MACHINES Herbert A. Silven, Worcester, Mass, assignor to Norton Company, .Worcester, Mass., a corporation of Massachusetts This invention relates to grinding machines, and more particularly to a mechanism for automatically controlling the rotative speed of a grinding wheel so as to maintain a substantially constant peripheral speed as the diameter of the wheel decreases due to wear.

In cylindrical grinding machines which have been heretofore produced and sold on the market, it has been customary to provide either a belt or a motor drive for the grinding wheel. The wheel spindle is either driven at a single speed during the entire life of the wheel or, in some cases, a two-stepped cone pulley has been F provided so that after the wheel had worn away 'to a predetermined extent, the operator might increase the speed (R. P. M.) so as to more nearly approach the correct peripheral speed of the wheel.

In grinding practice today, it is customary for a grinding wheel to be sold with a definite recommended speed of rotation. If the customer desired to obtain the maximum cutting efficiency for the wheel purchased, it must be rotated at the recommended speed. As the grinding operation proceeds, the grinding wheel wears away during use or is trued away periodically to recondition the surface, each of which reduce the diameter of thewheel. As the grinding wheel wears away, its diameter and its peripheral speed decrease so that the cutting efliciency of the wheel is continually being decreased. In production grinding in large manufacturing plants, it is common practice to utilize a wheel only until it has worn away to a given extent and then to either discard the remainder of the wheel or to have another machine upon which the wheel which is reduced beyond efiicient use on the first machine may be utilized. The speed of rotation of the second machine is increased so that the peripheral speed of the worn wheel, which has been changed to the second machine, will be substantially equal to the peripheral speed of theoriginal wheel when mounted on the first machine. By having several batteries 45? of machines: the first battery of machines, for

example, taking a 36" diameter wheel and wearing it down to 3-2", and then a second battery to take the 32 wheel and wear it away to 28", it is possible to use up the grinding wheel to the 50 maximum extent, without undue loss of efficiency. Even with such a practice, the maximum efficiency is not obtained, due to loss of time during wheel changes and also due to the fact that while in use on a given battery of machines, the peripheral speed of the grinding stantiaily constant peripheral speed of the grinding wheel during its entire life. By utilizing such a mechanism for maintaining a constant peripheral speed, it is possible to utilize the entire useful part of a grinding wheel, without the necessity of changing the wheel from one battery of machines to another after it has worn away to a predetermined extent.

It is the primary object of this invention to provide a suitable driving and speed controlling 15 mechanism for rotating a grinding wheel, which is automatically actuated as the wheel wears away to increase the speed of rotation of the wheel so as to maintain a substantially constant peripheral speed thereof. 20-

It is another object of this invention to provide a suitable means, which is controlled by movement of the slide supporting either the grinding wheel or the work piece, which automatically actuates a speed control device to ad- 2-5 vance the speed of rotation of the wheel as it wears away.

It is a further object of this invention to provide a grinding machine with a means controlled by movement of the work or wheel slideso as to 30 prevent the wheel from being rotated at other than a predetermined speed, but which allows the wheel to rotate at a higher speed as it dew creases in size.

It isa still further object of this invention to provide a speed regulating device for the grinding wheel which automatically reduces the rotative speed of grinding wheel speed before a new full-sized wheel may be mounted on the machine.

Other objects will be apparent from the fol- 40 lowing disclosure. As shown in the drawing, one embodiment of the invention has been illustrated in which like reference numerals indicate like parts:

Fig. l is a side elevation of a grinding machine,

speed controlling rheostat 5' position which automatically controls the maxi-' mum speed of rotation of the grinding wheel.

In the preferred construction, the grinding wheel is rotated by an electric motor of the variable speed type, and a suitable speed controlling 'rheostat is connected to regulate the speed of rotation The movement of the rheostat" of the motor. control lever is automatically actuated by transverse movement of the slide so that as the grinding wheel is worn away, the rotative speed of the 'wheel is increased automatically so as to maintudinally movable work carriage 2|.

tain a substantially constant peripheral speed of thegrinding wheel during its entire life.v The actuating mechanism for the speed controlling rheostat is preferably provided with a suitable lost motion connection, which permits the separation of the wheel and work through a distance normally required when separatingthev wheel and workto remove the finish ground piece of work and replace it witha new piece, without moving the speed, controlling rheostat. The actuating mechanism and speed controlling device are so arranged that when thegrinding wheel is worn away and must be replaced, the separating movement between the wheel and work to make room for a full-sized grinding wheel automatically turns the'rheostat in the reverse direction so that when the new, full-sized grinding wheel is mounted in place, it will be rotated at the proper speed.

As illustratedin the drawing, a grinding machine is provided having a base It) supporting a rotatable grinding wheel H, in suitable bearings |2 which are integrally supported on projections An electric motor I4 is fixedly |3 of the base l0. mounted on the base l0 and is connected by a driving belt.

spindle l6. v

A work supporting'carriage I8 is mounted for a transverse movement on slideways I9 and 20 on thebaselfl, The work slide may be fed transversely by any suitable feeding mechanism which,

;as shown in Fig. 1,.may comprise a half nut 23 depending from the slide I8; and meshing with a Y feed screw 2| which is journalled in suitable bearings (not shown) in the base In. The outer end of the feed screw is provided with a. hand wheel 22 -sothat the operator may manually rotate the screw andfeed the work slide toward and from the grinding wheel.

A cylindrical work. piece 25 is rotatably mounted on centers on the headstock (not shown) and a footstock 26 which are mounted on a longi- The carriage 2 1 is mounted to slide on a Vway 28 and a flat way 29 on the transversely movable work carriage] 8, andis provided with a rack 30 which meshes with a gear 3|. The gear 3| is mounted on the, end of a shaft 32 which is suitably journailed in bearings (not shown) in the work slide l8. 'The outer end of the shaft 32 is provided with a manually operable hand wheel 33 so that the operator may traverse the work carriage |5 to rotate the grinding wheel longitudinally of the machine to position the work relative to the grinding wheel or may cause the necessary relative reciprocation between the wheel and work during grinding, if desired. This longitudinal movement of the work relative to the grinding wheel may be accomplished by means of any of the well-known power driven reciprocating mechanisms but for the sake of simplicity of illustration, a manual adjustment for the carriage has been shown.

The grinding wheel rotating motor I4 is preferably of; a variable speed type which is connected to a suitable source. of power, as diagrammatically indicated by the power lines 35 and'36 which are connected through a rheostat 31 to regulate the speed of rotation of the motor 4.

In order to attain the primary object of this invention,a suitable mechanism is provided for actuating the rheostat control arm 38 automatically to increase the rotative speed of the grinding wheel I l as it wears away so as to maintain a substantially constant peripheral speed of thewheel during its entire useful life. The movable slide'is preferably provided with a rack bar 39, mounted on the lower side of the slide I8, meshing with a. gear 4|] which is rotatably mounted on a stud 4| which is fixedly mounted on'the base ID. A sprocket 45 is also rotatably mounted on the stud 4| and is connected by a link chain 46 to a sprocket 41 on the rheostat shaft 48. It will be readily appreciated that transverse movement of the slide |8 will operate through the rack 39, gear 40, sprocket 45, chain, sprocket 41 and shaft' 48 to rotate the control arm 38 of the rheostat 31, so as to vary the speed of the motor l4.

The gear and the sprocket may be integrally connected so that any movement of the transverse slide It! will be transmitted to the rheostat 31. In the preferred form, however, it is desirable to provide a suitable lost motion connection between the gear 40 and. the sprocket 45 which, as illustrated, comprises a pin 50 integral with and projecting from the gear 40. The pin 50 rides in a cut-out portion 5| (Fig. 3) in the hub 52 of sprocket 45. The length of the cut-out portion of the'gear 45 is sufllcient to allow normal separation of the wheel and. work after fin-' ish g'rinding one piece of work to enable the operator toremove the finish ground work and'to replace it with a new piece without disturbing or chan ing the speed of 'the wheel. As the operator feeds the workpiece 25toward the wheel by moving the slide I8, the rack 39 causes a rotation ofthe gear 40 and'pin 50 in a counterclockwise direction, as indicated in Fig. 1. V'I 'here is sufficient movement in the cut-out portion 5| so tate the rheostat control army or thereby automatically increase the speed of the motor and also the peripheral speed of the wheel H. ,The rheostat is preferably so constructed and so con nected through the 'gear and rackthat the advancing movement of the work slide toward thev wheel as the wheel wears away is sufficient to advance the rotative speed of the motor 14 soas sprocket 45 ismounted on a reduced portion 55 56 to maintain the sprocket in a fixed relation of the hub 52. A screw threaded collar 56, which is threaded onto-an extending portion of the hub 52, serves to lock the sprocket 45 in a fixed relation with the hub .52. By loosening the threaded collar 56 and rotating the sprocket 45, the sprocket controlling the rheostat may be adjusted to the desired extent to regulate the speed of the motor so as to rotate the grinding wheel at the desired rate. The operator then locks the collar withthe hub 52. The operation of the machine as the wheel Wears away will then automatically advance the rotative speed of the wheel as the wheel wears away and the work approaches nearer the axis of the wheel on successive grinding operations to maintain a substantially constant and uniform peripheral speed of the wheel.

This speed controlling apparatus is equally adapted for use in a plain cylindrical grinding machine of the type in which the grinding wheel is rotatably supported on a transversely movable wheel slide. Such a machine may comprise a base 10 (Fig. 4) supporting a rotatable wheel H which is mounted in suitable bearings 60 on a transversely movable wheel slide 6|. The grinding wheel H is rotated by a variable speed electric motor 62 which is mounted on the wheel slide BI and connected by means of a belt 63 to rotate a wheel spindle 64. A work supporting table 65 is slidably mounted on V-way 66 and fiat way 61 of the base I 0 and is arranged for longitudinal movement by a manually operable wheel 68 which is carried by the shaft 69. The shaft 69 carries a gear "l0 meshing with a rack H depending from the work slide 65.

The wheel slide may be fed toward and from the work piece by any of the well-known feeding mechanisms but for the sake of simplicity of illustration, a manually operable mechanism has been illustrated, comprising a manually operable feed wheel 11 mounted on a rotatable shaft 12. The shaft 12 carries a gear 13 meshing with a gear 14 on the front end of a feed screw 15 which is rotatably supported in bearings (not shown) in the base Ill. The feed screw 15 engages a half nut 16 depending from the wheel slide 6|. The speed controlling unit for regulating the speed of the electric motor 62 is actuated by a rack 18 on the wheel slide. The rheostat and the controlling mechanism therefor are identical with the illustration as shown in Fig. 1. Consequently, the mechanism is not described in detail in connection with Fig. 4. The parts forthe speed control are numbered to correspond with the similar parts previously illustrated and described in Figs. 1, 2, and 3.

The operation of this machine is readily apparent from the foregoing disclosure. The operator mounts a full-size abrasive wheel on the wheel spindle. The nut 56 is then loosened and the sprocket 45 rotated to adjust the rheostat so as to rotate the wheel at the desired speed. The grinding operation may then be started and, as previously explained, the lost motion connection in the gearing allows normal separation of the work and wheel without changing the speed of the wheel. As the wheel wears away due to normal wear or truing, the movable slide advances a greater distance towards the axis of the stationary member in grinding the work piece to a finished size. This further movement of the slide operates through the lost motion gearing to automatically advance the rheostat to increase the rotative speed of the wheel so as to maintain a substantially constant peripheral speed of the wheel as it wears away.

Having thus described the invention, what is claimed as new and desired to secureby Letters Patent is;

,1. A grinding machine comprising a base hav ing a rotatable work support and a rotatable grinding wheel thereon, means including a variable speedelectric motor to rotate said wheel, means including a rheostat to regulate the feed of said motor, a transversely movable slide carrying either the work supportor the grinding wheel for movement relatively toward and from each other, a feeding mechanism to feed said slide and cause a relative approaching and receding movement between the work support and wheel to grind successive work pieces to a predetermined size, driving connections between said slide and rheostat which are arranged so that movement of the slide to cause a relative approaching movement between the wheel and work support automatically actuates said rheostat during grinding to maintain a substantially constant peripheral speed of the wheel as it wears away, and a lost motion device in said driving connections whereby the normal transverse feeding movement between the wheel and work support during grinding does not affect said rheostat speed regulating means.

2. A cylindrical grinding machine comprising a base having a rotatable work support and a rotatable grinding wheel thereon, means including a. variable speed electric motor to rotate said wheel, means including a rheostat to regulate the speed of said motor, a transversely movable slide carrying either the work or the grinding wheel for movement relatively toward and from each other, a feeding mechanism to feed the slide and cause a relative approaching and receding movement between the work support and the wheel to grind successive work pieces to a predetermined size, and lost motion connections between the slide and rheostat which are arranged so that movement of the slide to cause a relative approaching movement between the wheel and Work support automatically actuates said rheostat during grinding to maintain a substantially constant peripheral speed of the wheel as it wears away, the lost motion of said gearing providing means whereby the normal transverse feeding movement between the grinding wheel and work support during grinding does not afiect said rheostat speed regulating means.

3. A cylindrical grinding machine comp-rising a base having a rotatable work support and a rotatable grinding wheel thereon, means including a variable speed electric motor to rotate said wheel, means including a rheostat to regulate the speed of said motor, a transversely movable slide carrying either the work support or the grinding wheel for movement relatively toward and from each other, a feeding mechanism to feed said slide and cause a relative approaching and receding movement between the work support and wheel to grind successive work pieces to a desired size, a rack carried by said slide, a lost motion gearing connecting said rack with the rheostat which is arranged so that movement of said slide to cause a relative approaching movement between the wheel and work support automatically actuates said rheostat during grinding to maintain a substantially constant peripheral speed of the wheel as it wears away, the lost motion of said gearing providing means whereby thenormal traverse feeding movement between the grinding wheel and work support during grinding does not affect the said rheostat speed regulating means.

4. A grinding machine comprising a. base having a work support and a rotatable grinding wheel thereon, means including a variable speed electric motor to rotate said wheeL means including a rheostat to regulate the speed of said motor, a transversely movable slide carrying eitherthe work support or the grinding wheel for movement relatively toward and from each other, arfeedingmechanism to move said slide alost motion'connection between said gear and sprocket, and a link chain connecting the.

sprocket with the rheostat to actuate the latter during grinding so as to automatically maintain a substantiallyconstant peripheral speed of the wheel during grinding as it wears away but permit normal movement of the slide towards and fromthe work without afiecting the wheel speed.

HERBERT A. SILV'EN. 

